Roofing granules and method of



iteiuu d Sept. 30, 1941 e s noon-mo 21.:1; GRANULES m ME'rnon rnonucmo sans Ernest E'Nichols, wnliamspo t. are.

No Drawing. Original No. 1,954,778. dated April 10, 1934, Serial No. 640,733, November 1, 1932.

Application for reissue May 21,

assasz 2 Claims.

This invention relates to new and useful im- 1940 Serial No.

provements in granular material, such as is D ill? clpally used as a surfacing for asphalt shingles and other forms of asphalt roofing, known as roofing granules, and more particularly to roofing granules having a glassy or vitrified surface. It has been found that, while'glazed granules present an attractive appearance and possess other favorable characteristics, they do not properly adhere to the asphalt base of which the roofing is composed, but become detached theregranule stock and which has, on that account,

been discarded as refuse, resulting .in considerable waste.

It is, therefore, an object of the invention to produce roofing granules of the glazed surface type, which will properly adhere to the surface of the roofing in connection with which they are used, and a further object to produce a method of manufacturing the same to eliminate the waste resulting from the grinding process, as far as possible.

In the manufacture of granules of the type to which this invention relates, the granule base or stock is formed of silica quartz, such as is found in the vicinity of Akron and Youngstown, Ohio, as this material possesses a proper degree of hardness, is not sufiiciently brittle to interfere with its being satisfactorily comminuted. and because of its high silica content, it will fuse readily.

Th quartz is first ground in a suitable crusher to reduce it to comparatively fine particles. It is then subjected to a screening operation to ob-,

tain those particles that will pass a No. 8 screen but are retained on a No. 35., and these particles are then set aside for use as the granule stock.

During the grinding process, to which it is customary tosubiect the material of which roofing granules are made, in order to produce the granule stock, it is impossible to prevent the production of considerable waste material, ranging from exceedingly fine powder to that which just succeeding in passing the retaining screen. Inthe present process, there is no such waste, as

this material is utilized in the manufacture of the finished product.

The otherwise waste material, to which refer ence has Just been made, is used in the making up of a surfacing mixture for coloring the granules and to provide a glazed, irregular surface thereon, in a manner now to be described. A suitable amount of this heretofore waste is placed in a pebble mill, together with proper portions of boric oxide and color oxide, according to the color desired, also a sufficient amount of water to dissolve boric oxide and insure proper grinding. Obviously boric oxide, which is known to have a solubility in water of between 1.1 and 16.4 grams in 100 cc. of water dependent on the temperature, is a water soluble chemical and it isfurther known that boric oxide is an excellent flux for silica or quartz. The mill is then operated to dissolve the boricoxide and to crush the coarser particles of the quartz to such a degree that it will allpass a No.- 60 screen. This quartz will then include sizes ranging from thefinest powder to those that just succeeded in passing the screen.

To the result is then added a sufficient amount of water to impart a proper consistency, thus completing the surfacing mixture. It has been found that a suitable surfacing mixture may be produced by using the following proportions: 45 pounds of the silica quartz; 6 pounds of borlc oxide; 50 pounds of color oxide; and an amount of water as explained. It may develop, however, that, under certain conditions, better results may be obtained by varying these proportions somewhat.

Having now produced the granule stock and Particular attention is here called to a most im-' portant feature of the present invention, namely, the fact that the coating with which each particle of the granule stock is now thoroughly covered, includes particles of the silica quartz rangingin size from exceedingly fine powder up to the sixty mesh size.

After the excess surfacing mixture has been drawn from the mixer, the stock is permitted to pass from thelatter, through a suitable chute into the higher end 'of an inclined rotary kiln, the.

heating element of which, preferably an oil bumer, is so controlled asto provide within the kiln an atmosphere which is divided into approximatethe second or vitrifying zone.

end, being maintained at approximately 1200" F.

Owing to the rotation of the kiln, the stock, during its passage therethrough, which passage is brought about by the inclination thereof, is constantly agitated, so that its particles are evenly subjected to the temperature within the various zones, on all sides, and will not fuse together.

Upon passing through the first zone, the stock becomes thoroughly dry. It next passes through Here the finer particles of the silica quartz contained within the surface coating become completely melted andform a fluid which mixes with the borlc oxide and color oxide. The larger particles of the silica quartz, owing to their greater size, do not completely melt down, however, before passing from this citrifying zone, but fuse on their surfaces only. As a result, they do not so mix with the melted finer particles as to completely lose their identity, but remain suspended therein. This surface fusing of the larger particles, will however, be sufiicient to take up a proper amount of the color oxide and boric oxide, so that the entire surface of the completed granules will possess an even color and the characteristics resulting from the use of the boric oxide. As the surface of each particle of the granule stock will also have become fused to a degree, the now fused surfacing mixture will firmly adhere thereto.

Having been thus coated, the stock, before emerging from the kiln, now passes through the thir zone which, being of a somewhat lower temperature than the vitrii'ying zone, prevents too sudden cooling of thestock. Having traversed this zone, the stock passes from the lower end of the kiln into and through a suitable rotary cooler where its temperature is reduced to the proper degree and from this cooler the now completed roofing granules pass to storage.

It will be'understood that the degree of inclination of the kiln must be. such as to cause the stock to consume such a length of time, in passing through the various heat zones, as will produce the results herein outlined. This is particularly true with respect to the central or vitrifying zone, as the stock mustpass therefrom before the larger particles of quartz in the suriacing mixture have become completely melted.

Because of the failure of these larger particles to completely melt down into and mix with the faces of these larger particles, having taken up a proper amount of the color oxide and the boric oxide, as has also the surrounding surface, the entire surface of each finished granule is not only evenly glazed but also evenly colored and a proper degree of toughness, the latter characteristic being due to' the use of boric oxide.

It will be understood that the portion of the ever in the manufacture of roofing granules underthis method. Due to the elimination of this waste, and the saving resulting from the use of otherwise waste material for surface glazing, so that it is not necessary to purchase special material for that purpose, as is customary under other methods, it will be seen that the cost of manufacture has been reduced materially and that,,at the same time, a processhas been developed for producing roofing granules that possess great durability, that are evenly and brilliantly colored and, while being highly glazed, are so formed as to insure their proper adherence to an asphalt surface. v

Whatis claimed is: 1. A method of making roofing granules which consists of first producing granule nuclei by crushingvitreous material and separating certain large sizes thereof from the smaller sizes,.

crushing the smaller sizes to produce differing sizes relatively much smaller than, the granule nuclei, applying to each particle of the granule nuclei a coating including a flux and said differing sizes, then firing the coated nuclei at such a temperature and for such a time as to fuse the,

surfaces only of the nuclei particles, as to completely fuse the smaller particles of the coating, and as to partly fuse the larger sizes of" the coating.

2. A method of making, roofing granules of quartzitic material which consists of crushing the material, separating from the larger particles of the crushed material certain particles of a predeterminedsize for use as granule nuclei and the smaller particles, regrinding the smaller particles to produce particles of much smaller size than the nuclei particles and of differing sizes, mixing with the reground particles a flux, a color oxide, and water to form a coating composition, coating the nuclei-particles with said composition, subjecting the coated particles to a drying process, and heating the coating and dried particles to a temperature and for a time suilicient to use the surfaces'only of the nuclei particles and to fuse the coating particles to each other and to the nuclei particle.

ERNEST H. NICHOLS. 

